1. Field of the Invention
The invention relates a gas engine, especially a diesel gas engine, with a control system for controlling and regulating the gas engine in dependence on changing limiting conditions. More specifically, the invention relates to a gas engine with a pilot control device which receives measurements of the limiting conditions, calculates output signals, and transmits the output signals to activators which activate final control elements for adjusting the engine operating point to the changed limiting conditions.
2. Description of the Related Art
Modern gas engines that operate on the lean-burn principle are able to comply with the standards for NOx emissions (e.g., those based in Germany on T A Luft) without requiring exhaust gas after treatment, even at high mean pressures. One prerequisite for meeting the standards for NOx emissions is a lean gas-air mixture, which requires a high air-fuel ratio .lambda. in the combustion chamber (lean-burn method).
The engine must therefore be kept within a narrow operating range at all limiting conditions (ambient temperature, ambient pressures, gas qualities, etc.). The operating range is limited, on the one hand, by the knocking limit or toxic emissions standards and, on the other hand, by the lean-operation limit. Moreover, the operating range depends on the output, and within the possible operating range optimum efficiency is to be attained. These physical relationships apply for diesel gas engines based on the diesel gas principle as well as to pilot injection gas engines and spark ignition gas engines, in all cases with or without prechamber ignition.
Various methods of keeping the engine in the preestablished operating range are known from the prior art. These methods include knocking control, ignition failure control, .lambda. control, and methane measurement probes.
The use of these methods is disadvantageous in that their use is limited during changes in the limiting conditions. In addition, there are essential disadvantages due to the inherent physical principles of the methods of knocking control and ignition failure control.
For example, knocking control devices do not become active until the engine is already in knocking operation. However, the operating state bordering directly on the knocking limit places engines, especially engines with high mean pressures (&gt;16 bar), under high mechanical and thermal stresses. Generally, the limits on NOx emissions cannot be complied with during knock-controlled operation. Similarly, ignition failure recognition devices cannot respond until actual ignition failure occurs. In such an operating state, however, a considerable loss in efficiency has already taken place.
During changes in limiting conditions such, for example, as fluctuations in the amount of methane or the charging air temperature/mixture temperature before the cylinder, the adjustment of the air-fuel ratio by .lambda.-control ensures neither compliance with NOx emission standards (lean-operation limit) nor maintenance of a sufficient distance from the top limit.
Another important influence on the NOx emissions and knocking limit operating parameters is the properties of the combustible gas. Therefore, a sensor that detects the combustible gas properties may be used to control the engine operating parameters.
A prior art gas engine with a control and regulating system for controlling the gas engine in response to changes in the limiting conditions is known from the article "Influence of methane number on combustion in the spark ignition gas engine" ["Einfluss der Methanzahl auf die Verbrennung im Gas-Ottomotor"] in Motortechnischen Zeitschift 54 (1993), pp. 350 ff. A disadvantage of the control and regulating concept described in this article is that although the described pilot control device ensures compliance with desired emission limits by controlled operation in methane ranges wherein the knocking limit has not yet been reached, the control device does not prevent the engine from reaching the knocking limit or being driven into a knocking operation state.